A semiconductor device manufacturing process includes a process for forming a film by, e.g., CVD (Chemical Vapor Deposition), by supplying a gas to a semiconductor wafer (hereinafter, referred to as a “wafer”) or a process for etching the film on a surface of the wafer by a gas supplied to the wafer. A film forming apparatus or an etching apparatus for performing the above-described process includes a processing chamber for accommodating a wafer, a storage unit for storing a processing gas used for film formation or etching, and a storage unit for storing a cleaning gas for dry cleaning an interior of the processing chamber. The storage units for storing such gases and the processing chamber are connected through a gas supply device including gas supply lines, valves disposed in the gas supply lines, or the like.
In order to ensure a high corrosion resistance, the gas supply device is made of, e.g., stainless steel. Further, a filter for removing solid or liquid particles contained in gases may be disposed in the gas supply lines.
For the film forming apparatus or the etching apparatus, highly reactive halogen-containing gases referred to as an F (fluorine)-based gas, a Cl (chlorine)-based gas and a Br (bromine)-based gas respectively containing F, Cl and Br may be used. For example, the F-based gas may be used as a cleaning gas in the film forming apparatus. The Cl-based gas and the Br-based gas may be used as etching gases in the etching apparatus.
The halogen-containing gases react with stainless steel forming the gas supply device for supplying such gases, thereby generating a ternary compound containing halogen, metal and oxygen and a binary compound containing halogen and metal. These compounds cause metal contamination of the gas. A ternary compound and a binary compound, each having a high vapor pressure, flow in a gaseous state through the gas supply lines, and thus are supplied into the processing chamber without being trapped by the filter. The ternary compound and the binary compound are decomposed by exposure to an atmosphere in the processing chamber, so that metals contained in these compounds may be solidified and adhered to the wafer and the processing chamber. If so, the wafer is not normally processed, and the production yield may be decreased.
The gas supplied to the processing chamber is introduced into the gas exhaust line for exhausting the processing chamber. When the interior of the gas exhaust line becomes a low vacuum region where a gas pressure is high and the collisions between gas molecules are more dominant than the collisions between gas molecules and the pipe wall of the gas exhaust line, the flow velocity of the gas in the gas exhaust line is highest at the central axis of the gas exhaust line, and is decreased as it goes close to the pipe wall of the gas exhaust line from the central axis thereof, and becomes zero at the pipe wall. The gas may be diffused toward the upstream side, i.e., toward the processing chamber, along the pipe wall at which the flow velocity is zero. When the gas is diffused toward the processing chamber as described above, the ternary compound and the binary compound in the gaseous state are converted into compounds containing solid metals and then are adhered to the wafer or the processing chamber, which may lead to a decrease in the production yield. Further, a sub-device such as a vacuum gauge or the like may be attached to the processing chamber via an auxiliary passage. In a line forming the auxiliary passage as well as in the gas exhaust line, the gas may be diffused toward the processing chamber from the pipe wall at which the flow velocity is zero. Moreover, the gas may be diffused toward the processing chamber from the sub-device side due to changes in the pressure in the processing chamber. Even when the gas is diffused from the auxiliary passage, the ternary compound and the binary compound in the gaseous state may be converted into compounds containing solid metals and then adhered to the wafer or the processing chamber.
In order to prevent the decrease in the production yield caused by the above-described phenomenon, the following processes are carried out: the halogen-containing gas is supplied into the processing chamber; a dummy wafer (wafer that is not a product wafer) is transferred into the processing chamber and subjected to etching or film formation; the dummy wafer to which the metal is adhered is unloaded from the processing chamber; and a normal wafer is transferred into the processing chamber and subjected to etching or film formation. Or, the following processes may be carried out: a predetermined gas is supplied into the processing chamber; a film that covers the metal adhered to the wall surface of the processing chamber to prevent scattering of the metal is formed; and the wafer is transferred into the processing chamber and subjected to treatment. However, even when the dummy wafer is used or when the scattering prevention film is formed in the processing chamber, the processes which do not contribute to the fabrication of semiconductors are performed. Therefore, the throughput is decreased, and the processing cost is increased.
Japanese Patent Application Publication No. 2002-222807 discloses a technique for preventing metal contamination of a wafer by coating a metal member that contacts a gas with chromium oxide. However, the halogen-containing gas reacts with chromium oxide, so that the above-described problems cannot be solved.